1. Field of the Invention
The present invention relates to a reservoir tank attached to an axle driving system in which a hydrostatic transmission (hereafter referred to as HST), an axle, and a drive train for connecting the HST and the axle for driving are housed in a common housing.
2. Related Art
Conventionally, a housing that houses an HST is filled with hydraulic oil that is also used as lubricating oil. A temperature of the hydraulic oil is increased by driving the HST. The increase in temperature of the hydraulic oil results in an increase in its volume. In order to receive the increase in the volume, a technique of providing a reservoir tank on an outside of the housing or forming space having a volume corresponding to the increase within the housing to form a reservoir room is known.
For example, there is a technique disclosed in U.S. Pat. No. 4,987,796 or U.S. Pat. No. 5,440,951.
However, an axle driving apparatus that utilizes a reservoir tank structure. requires additional space, a mounting member for mounting the reservoir tank, and piping for connecting the reservoir tank and the housing. In addition, the number of man-hours required for assembly increases, the reservoir tank is difficult to handle, and cost increases.
By positioning the reservoir tank at an upper portion of the housing, a vertical length of the housing increases to inhibit miniaturization of the axle driving system and an air layer is created in the housing to cause air to be swallowed in oil when the oil within the housing is stirred. If this oil is charged into a closed circuit of the HST as the hydraulic oil, volume efficiency of the HST is reduced, which may generate noise or reduce durability.
Further, it is difficult to integrally form the reservoir tank at the upper portion of the housing for a lawn tractor having a rear discharge method, because a chute passes above the axle driving system.